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40 A MODIFIED CLAY AS ADSORBENT OF AN ORGANIC POLLUTANT IN AQUEOUS AND MIXED SOLVENT SYSTEMS Valentine Nzengung, Graduate Research Assistant Voudrais Evangelos, Assistant Professor Department of Environmental Engineering School of Civil Engineering Marion Wampler, Associate Professor Department of Geochemistry School of Earth and Atmospheric Sciences Georgia Institute of Technology Atlanta, Georgia 30332 INTRODUCTION Natural clays are ineffective adsorbents for poorly water-soluble organic contaminants such as hydrophobic organic chemicals (HOCs), which are some of the pollutants transported from contaminated sites and petroleum spills into the subsurface environment and groundwaters.1-8 Clay minerals possess a net negative electrical charge compensated for by inorganic exchange ions, (e.g., Na, and Ca), which are strongly hydrated in the presence of water. This results in hydrophilic (water loving) environment on the clay surface. The surface properties of natural clays can be modified by simple ion-exchange reactions. Smectites (Montmorillonite clays) are easily modified by exchanging inorganic cations with alkylammonium cations also called quaternary ammonium cations (QUATS). By modifying clays in this manner the inter-lamellar spacing is increased and the adsorptive surfaces of the clays are opened up to enhance adsorption of organic molecules.1-4'9 More importantly, the substitution by organic cations reduces the hydration of the clay and simultaneously decreases the "free" aluminosilicate mineral surface area (i.e., the surface not covered by the organic exchange ions). As the inorganic ions are progressively replaced by the organic cations, the surface properties of a clay containing mainly inorganic ions may change considerably from highly hydrophilic to increasingly organophilic (hydrophobic). The organic cations used commercially in the ion exchange process are almost exclusively alkylammonium salts (ALAS) with one or two long chain alkyl or aryl groups, i.e. they are cationic surfactants.10 Their classification as such is because in aqueous solution each molecule has a nonpolar hydrocarbon group and a cationic, polar group. The molecular structures of these ALAS are diverse. Depending on the hydrophobicity of the "tail", or R-group, the clays resulting from the exchange reactions may be classified into two categories:2-4 (1) Organophilic clays produced from ALAS with relatively long aliphatic R-groups. This may be represented by hexadecyltrimethylammonium (HDTMA-), and Benzyldimethyltetradecylammonium (BDTDA-) smectites, where R is C16 and C,8 hydrocarbons. (2) Adsorptive clays, produced from ALAS with relatively short (less complex) Regroups.7'12 This may be represented by tetramethylammonium (TMA-) and trimethylphenylammo- nium (TMPA-) smectites, where R is C4 and C9, respectively. Adsorption studies from aqueous solution with natural smectite and organo-smectites as adsorbents have been performed with a variety of HOCs. Boyd et al.3,4 and Jaynes and Boyd13 showed adsorption on the mineral surfaces was suppressed by water, and the uptake of nonionic organic chemicals (NOCs) by HDTMA-smectite is essentially due to solute partitioning into the organic phase created from the large C16 alkyl groups of HDTMA ions interacting with the clay. The organic matter derived from exchanged HDTMA was 10 to 30 times more effective than natural soil organic matter in the uptake (partition) of benzene, dichlorobenzene, and tetrachloroethylene from water.3,4 In many waste-disposal sites and in industrial wastewater treatment systems, there are solvents aiding in mobilizing sparingly soluble organics. To analyze the sorption of HOCs from aqueous- 48th Purdue Industrial Waste Conference Proceedings, 1993 Lewis Publishers, Chelsea, Michigan 48118. Printed in U.S.A. 387
Object Description
Purdue Identification Number | ETRIWC199340 |
Title | Modified clay as adsorbent of an organic pollutant in aqueous and mixed solvent systems |
Author |
Nzengung, Valentine Evangelos, Voudrais Wampler, Marion |
Date of Original | 1993 |
Conference Title | Proceedings of the 48th Industrial Waste Conference |
Conference Front Matter (copy and paste) | http://earchives.lib.purdue.edu/u?/engext,21159 |
Extent of Original | p. 387-392 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital object copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
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Date Digitized | 2009-11-10 |
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Color Depth | 8 bit |
Description
Title | page 387 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital object copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Transcript | 40 A MODIFIED CLAY AS ADSORBENT OF AN ORGANIC POLLUTANT IN AQUEOUS AND MIXED SOLVENT SYSTEMS Valentine Nzengung, Graduate Research Assistant Voudrais Evangelos, Assistant Professor Department of Environmental Engineering School of Civil Engineering Marion Wampler, Associate Professor Department of Geochemistry School of Earth and Atmospheric Sciences Georgia Institute of Technology Atlanta, Georgia 30332 INTRODUCTION Natural clays are ineffective adsorbents for poorly water-soluble organic contaminants such as hydrophobic organic chemicals (HOCs), which are some of the pollutants transported from contaminated sites and petroleum spills into the subsurface environment and groundwaters.1-8 Clay minerals possess a net negative electrical charge compensated for by inorganic exchange ions, (e.g., Na, and Ca), which are strongly hydrated in the presence of water. This results in hydrophilic (water loving) environment on the clay surface. The surface properties of natural clays can be modified by simple ion-exchange reactions. Smectites (Montmorillonite clays) are easily modified by exchanging inorganic cations with alkylammonium cations also called quaternary ammonium cations (QUATS). By modifying clays in this manner the inter-lamellar spacing is increased and the adsorptive surfaces of the clays are opened up to enhance adsorption of organic molecules.1-4'9 More importantly, the substitution by organic cations reduces the hydration of the clay and simultaneously decreases the "free" aluminosilicate mineral surface area (i.e., the surface not covered by the organic exchange ions). As the inorganic ions are progressively replaced by the organic cations, the surface properties of a clay containing mainly inorganic ions may change considerably from highly hydrophilic to increasingly organophilic (hydrophobic). The organic cations used commercially in the ion exchange process are almost exclusively alkylammonium salts (ALAS) with one or two long chain alkyl or aryl groups, i.e. they are cationic surfactants.10 Their classification as such is because in aqueous solution each molecule has a nonpolar hydrocarbon group and a cationic, polar group. The molecular structures of these ALAS are diverse. Depending on the hydrophobicity of the "tail", or R-group, the clays resulting from the exchange reactions may be classified into two categories:2-4 (1) Organophilic clays produced from ALAS with relatively long aliphatic R-groups. This may be represented by hexadecyltrimethylammonium (HDTMA-), and Benzyldimethyltetradecylammonium (BDTDA-) smectites, where R is C16 and C,8 hydrocarbons. (2) Adsorptive clays, produced from ALAS with relatively short (less complex) Regroups.7'12 This may be represented by tetramethylammonium (TMA-) and trimethylphenylammo- nium (TMPA-) smectites, where R is C4 and C9, respectively. Adsorption studies from aqueous solution with natural smectite and organo-smectites as adsorbents have been performed with a variety of HOCs. Boyd et al.3,4 and Jaynes and Boyd13 showed adsorption on the mineral surfaces was suppressed by water, and the uptake of nonionic organic chemicals (NOCs) by HDTMA-smectite is essentially due to solute partitioning into the organic phase created from the large C16 alkyl groups of HDTMA ions interacting with the clay. The organic matter derived from exchanged HDTMA was 10 to 30 times more effective than natural soil organic matter in the uptake (partition) of benzene, dichlorobenzene, and tetrachloroethylene from water.3,4 In many waste-disposal sites and in industrial wastewater treatment systems, there are solvents aiding in mobilizing sparingly soluble organics. To analyze the sorption of HOCs from aqueous- 48th Purdue Industrial Waste Conference Proceedings, 1993 Lewis Publishers, Chelsea, Michigan 48118. Printed in U.S.A. 387 |
Resolution | 300 ppi |
Color Depth | 8 bit |
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